Display device

ABSTRACT

According to one embodiment, a display device includes first and second substrates, and liquid crystal layer. The first substrate includes first and second electrodes. The second electrode includes comblike electrodes extending in parallel to a first direction and tapered toward tips thereof, and a connecting portion which connects the comblike electrodes. An initial alignment direction is parallel to the first direction or a direction orthogonal to the first direction. The comblike electrode includes a first part having sides each form a first angle with the first direction, and a second part having sides each form a second angle with the first direction, the second angle being greater than the first angle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and is based upon U.S. applicationSer. No. 14/817,382, filed Aug. 4, 2015, which claims the benefit ofpriority from Japanese Patent Application No. 2014-172373, filed Aug.27, 2014; the entire contents of which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to a display device.

BACKGROUND

An in-plane-switching (IPS) mode liquid crystal display device is knownas an example of display devices. An IPS mode liquid crystal displaydevice includes a pair of substrates used to seal a liquid crystal layertherein, and a pixel electrode and a common electrode are provided withone of the substrate. In the IPS mode liquid crystal display device, atransverse field produced between these electrodes is used to controlthe alignment of the liquid crystal molecules in the liquid crystallayer. Further, a fringe field switching (FFS) mode liquid crystaldisplay device is commercially used. In an FFS mode liquid crystaldisplay device, a pixel electrode and a common electrode are arranged ondifferent layers and a fringe field produced therebetween is used tocontrol the liquid crystal molecules.

Here, a high-speed transverse field mode liquid crystal display deviceis known as a liquid crystal display device with faster response andimproved alignment stability as compared to the conventional FFS modeone. In the high-speed transverse field mode liquid crystal displaydevice, a pixel electrode and a common electrode are arranged indifferent layers and a slit is provided with the electrode which iscloser to the liquid crystal layer to rotate the liquid crystalmolecules in the proximity of the sides of the slit facing each other inits width direction such that the liquid crystal molecules at one sideand the liquid crystal molecules at the other side are rotated inreverse.

As to such a high-speed transverse field mode liquid crystal displaydevice, further improvement of the alignment stability is demanded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view which shows a part of the structure ofa liquid crystal display device of a first embodiment.

FIG. 2 schematically shows a shape example applicable to a secondelectrode shown in FIG. 1.

FIG. 3 schematically shows a shape example applicable to a firstelectrode shown in FIG. 1.

FIG. 4 is a plan view which shows a layout example of a subpixelcomposed of the second electrode shown in FIG. 2 and the first electrodeshown in FIG. 3.

FIG. 5 is a view used for explanation of a high-speed transverse fieldmode and shows a part of the second electrode and an initial alignmentstate of liquid crystal molecules in a liquid crystal layer.

FIG. 6 is a view used for explanation of the high-speed transverse fieldmode and shows equipotential lines in the liquid crystal layer.

FIG. 7 is a view used for explanation of the high-speed transverse fieldmode and shows an alignment state of liquid crystal molecules in anon-state.

FIG. 8 is a view used for explanation of the high-speed transverse fieldmode and shows luminosity distribution of light passing through asubpixel in the on-state.

FIG. 9 schematically shows a shape of comblike electrodes in oneembodiment.

FIG. 10 is a cross-sectional view which shows a part of the structure ofa liquid crystal display device of a second embodiment.

FIG. 11 schematically shows a shape example applicable to a firstelectrode shown in FIG. 10.

FIG. 12 schematically shows a shape example applicable to a secondelectrode shown in FIG. 10.

FIG. 13 shows an example of a second electrode having a single-edgedstructure.

FIG. 14 shows a variation of a shape applicable to comblike electrodes.

FIG. 15 shows another variation of a shape applicable to the comblikeelectrodes.

DETAILED DESCRIPTION

In general, according to one embodiment, a display device includes afirst substrate, a second substrate, and a liquid crystal layer. Thefirst substrate includes a first electrode, an insulating layer coveringthe first electrode, a second electrode opposed to the first electrodewith the insulating layer interposed therebetween, and a first alignmentfilm covering the second electrode. The second substrate includes asecond alignment film opposed to the first alignment film. The liquidcrystal layer includes liquid crystal molecules sealed between the firstalignment film and the second alignment film. The second electrodeincludes a plurality of comblike electrodes extending in parallel to afirst direction and tapered toward tips thereof, and a connectingportion which connects the comblike electrodes. An initial alignmentdirection of the liquid crystal molecules is parallel to the firstdirection or a second direction which is orthogonal to the firstdirection. The comblike electrode includes a first part having sidesopposed to each other in the second direction each form a first anglewith the first direction, and a second part having sides opposed to eachother in the second direction each form a second angle with the firstdirection, the second angle being greater than the first angle.

Embodiments are described with reference to accompanying drawings.

Note that the disclosure is presented for the sake of exemplification,and any modification and variation conceived within the scope and spiritof the invention by a person having ordinary skill in the art arenaturally encompassed in the scope of invention of the presentapplication. Furthermore, a width, thickness, shape, and the like ofeach element are depicted schematically in the Figures as compared toactual embodiments for the sake of simpler explanation, and they are notto limit the interpretation of the invention of the present application.Furthermore, in the description and figures of the present application,structural elements having the same or similar functions will bereferred to by the same reference numbers and detailed explanations ofthem that are considered redundant may be omitted.

First Embodiment

FIG. 1 is a cross-sectional view which shows a part of a liquid crystaldisplay device DSP1 of the first embodiment. The liquid crystal displaydevice DSP1 includes, for example, a transmissive display panel PNL ofactive matrix type.

The display panel PNL includes a plurality of unit pixels PX in adisplay area DA used for image display. A unit pixel PX is a minimumunit of a color image displayed on the display area DA, and includes aplurality of subpixels SPX corresponding to different colors. In theexample of FIG. 1, a unit pixel PX is composed of subpixels SPXR, SPXG,and SPXB corresponding to red, green, and blue arranged in a firstdirection X. Note that a unit pixel PX may include a subpixel SPXcorresponding to white in addition to subpixels SPXR, SPXG, and SPXB.

The display panel PNL includes an array substrate AR, counter substrateCT arranged to be opposed to the array substrate AR, and liquid crystallayer LQ sealed in the array substrate AR and the counter substrate CT.In the present embodiment, liquid crystal molecules included in theliquid crystal layer LQ possess positive dielectric anisotropy.

The array substrate AR includes a first insulating substrate 10 such asa light transmissive glass substrate or resin substrate. The firstinsulating substrate 10 has a first main surface 10A opposed to thecounter substrate CT and a second main surface 10B opposite to the firstmain surface 10A.

Furthermore, the array substrate AR includes, at the first main surface10A side of the first insulating substrate 10, a switching element SW,first electrode E1 (lower electrode), second electrode E2 (upperelectrode), first insulating layer 11, second insulating layer 12, andfirst alignment film AL1.

A switching element SW and a first electrode E1 are disposed on asubpixel SPX. The switching element SW is provided with the first mainsurface 10A of the first insulating substrate 10 and is covered with thefirst insulating layer 11. The first electrode E1 is formed on the firstinsulating layer 11. Furthermore, in each subpixel SPX, the firstelectrode E1 is electrically connected to the switching element SWthrough a contact hole CH1 provided with the first insulating layer 11.

The first electrode E1 is provided to correspond to each subpixel SPX.The first electrode E1 is covered with the second insulating layer 12.The second electrode E2 is formed on the second insulating layer 12 andfaces the first electrode E1. In the example of FIG. 1, the secondelectrode E2 is shared by the subpixels SPX and has a plurality of slitsSL positioned to be opposed to the first electrode E1 of each subpixelSPX.

In the present embodiment, the first electrode E1 functions as a pixelelectrode used to selectively supply a voltage to its correspondingsubpixel SPX, and the second electrode E2 functions as a commonelectrode used to supply a common voltage to its corresponding subpixelSPX. The first electrode E1 and the second electrode E2 are formed of atransparent conductive material such as indium tin oxide (ITO) or indiumzinc oxide (IZO).

The first alignment film AL1 covers the second electrode E2 and contactsthe liquid crystal layer LQ. An alignment treatment such as rubbingtreatment or optical alignment treatment has been performed to the firstalignment film AL1.

Conversely, the counter substrate CT includes a second insulatingsubstrate 20 such as light transmissive glass substrate or resinsubstrate. The second insulating substrate 20 has a first main surface20A opposed to the array substrate AR and a second main surface 20Bopposite to the first main surface 20A.

Furthermore, the counter substrate CT includes, at the first mainsurface 20A side of the second insulating substrate 20, color filters21R, 21G, and 21B, black matrix 22, overcoat layer 23, and secondalignment film AL2.

Color filter 21R is formed of, for example, a resin material painted redand is arranged to correspond to the red subpixel SPXR. Color filter 21Gis formed of, for example, a resin material painted green and isarranged to correspond to the green subpixel SPXG. Color filter 21B isformed of, for example, a resin material painted blue and is arranged tocorrespond to the blue subpixel SPXB.

The black matrix 22 defines subpixels SPXR, SPXG, and SPXB. Boundariesof color filters 21R, 21G, and 21B overlap the black matrix 22. Theovercoat layer 23 covers color filters 21R, 21G, and 21B and evens thesurfaces of color filters 21R, 21G, and 21B.

The second alignment film AL2 covers the overcoat layer 23 and contactsthe liquid crystal layer LQ. As with the first alignment film AL1, analignment treatment such as a rubbing treatment or an optical alignmenttreatment has been performed to the second alignment film AL2.

On the outer surface of the array substrate AR, that is, on the secondmain surface 10B of the first insulating substrate 10, a first opticalelement OD1 including a first polarizer PL1 is disposed. Furthermore, onthe outer surface of the counter substrate CT, that is, on the secondmain surface 20B of the second insulating substrate 20, a second opticalelement OD2 including a second polarizer PL2 is disposed. A firstpolarization axis (first absorption axis) of the first polarizer PL1 anda second polarization axis (second absorption axis) of the secondpolarizer PL2 are orthogonal to each other as in a crossed-Nicolrelationship.

The liquid crystal display device DSP1 with the above structureselectively transmits incident light from the first optical element OD1through subpixels SPX to display an image on in the display area DA.

FIG. 2 schematically shows a shape example of the second electrode E2 ofFIG. 1. The second electrode E2 as depicted includes a plurality ofapertures AP. Apertures AP are arranged to face the first electrodes E1of the subpixels SPX.

Each aperture AP is defined by a connecting portion 3 extending in asecond direction Y which crosses the first direction X and a connectingportion 4 extending in the first direction X. In the example of FIG. 2,the second direction Y is orthogonal to the first direction X. From theconnecting portion 3, a plurality of comblike electrodes 5 (5 a, 5 b)extend toward the center axis of the aperture AP.

Note that, in the example of FIG. 2, comblike electrodes are formed in adouble-edged manner such that comblike electrodes 5 a extend from a sideof the connecting portion 3 (right edge) in the first direction X andcomblike electrodes 5 b extend from the other side of the connectingportion 3 (left edge) in the first direction X counter to the comblikeelectrodes 5 a.

Both comblike electrodes 5 a and 5 b extend parallel to the firstdirection X and are tapered toward their tips. Comblike electrodes 5 aextending from one connecting portion 3 are arranged with certainintervals along the second direction Y. Furthermore, comblike electrodes5 b extending from one connecting portion 3 are arranged with certainintervals along the second direction Y. Spaces defined by comblikeelectrodes 5 a and spaces defined by comblike electrodes 5 b correspondto the slits SL. The slits SL are formed parallel to the first directionX as with comblike electrodes 5 a and 5 b.

In the example of FIG. 2, comblike electrodes 5 a and 5 b are formed inthe same shape, and an arrangement pitch of each of comblike electrodes5 a adjacent in the second direction Y and an arrangement pitch of eachof comblike electrodes 5 b adjacent in the second direction Y are thesame. Comblike electrodes 5 a and 5 b are arranged alternately in thesecond direction Y.

Note that comblike electrodes 5 a and 5 b may be formed in differentshapes with different arrangement pitches. Furthermore, comblikeelectrodes 5 a and 5 b may not be arranged alternately in the seconddirection Y but may be arranged on single straight lines parallel toeach other in the first direction X.

FIG. 3 schematically shows a shape example of the first electrode E1 ofFIG. 1. In this example, the first electrode E1 is formed in a flatpanel shape without a slit or the like formed thereon, and issubstantially a rectangle of which side along the first direction X isshorter than its side along the second direction Y. Furthermore, in theexample depicted, the first electrode E1 includes a contact portion 6used for the electric connection to the switching element SW.

FIG. 4 is a plan view which shows a layout example of a subpixel SPXcomposed of the second electrode E2 of FIG. 2 and the first electrode E1of FIG. 3. In the example depicted, the area of the subpixel SPX isdefined by gate lines G1 and G2 extending parallel to each other in thefirst direction X and source lines S1 and S2 extending parallel to eachother in the second direction Y.

The switching element SW includes a semiconductor layer SC, gateelectrode GE, and relay electrode RE. One end of the semiconductor layerSC is electrically connected to source line S1 and the other end of thesemiconductor layer SC is electrically connected to the relay electrodeRE. Between these ends, the semiconductor layer SC faces the gateelectrode GE. The gate electrode GE is formed integrally with gate lineG1, for example. The relay electrode RE is electrically connected to thecontact portion 6 of the first electrode E1 through the contact holeCH1.

In FIG. 4, alternate long and short dashed lines indicate the edge ofthe black matrix 22. That is, the black matrix 22 is opposed to gatelines G1 and G2, source lines S1 and S2, switching element SW, andcontact portion 6. The black matrix 22 forms a pixel opening 22 a withinthe area surrounded by gate lines G1 and G2 and source lines S1 and S2.

The comblike electrodes 5 a and 5 b of the second electrode E2 extendwithin the pixel opening 22 a. Note that depiction of the connectingportion 3 and the connecting portion 4 is omitted from FIG. 4.

The first alignment film AL1 in FIG. 1 has been subjected to analignment treatment to align the molecules in an alignment treatmentdirection AD which is parallel to the first direction X. On the otherhand, the second alignment film AL2 has been subjected to an alignmenttreatment to align the molecules in the alignment treatment direction ADor in the opposite direction. That is, in the liquid crystal displaydevice DSP1 of the present embodiment, the direction in which thecomblike electrodes 5 a and 5 b and the slits SL extend and thealignment treatment direction AD (initial alignment direction of theliquid crystal molecules) are substantially the same.

As explained above, the first electrode E1 and the second electrode E2are opposed to each other with the second insulating layer 12 interposedtherebetween, and the comblike electrodes 5 are provided with the secondelectrode E2 which is positioned as the liquid crystal layer LQ side insuch a manner that the comblike electrodes 5 and the slits SL extend toconform to the alignment treatment direction AD. With this structure, ahigh-speed transverse field mode with faster response as compared to aconventional FFS mode can be achieved in the present embodiment. Theresponse speed mentioned here will be defined as a speed of transitionof light transmissivity of the liquid crystal layer LQ within certaindegrees by applying a voltage between the first electrode E1 and thesecond electrode E2.

A principle of the high-speed transverse field mode will be explainedwith reference to FIGS. 5 to 8. Note that FIGS. 5 to 8 are only used forthe explanation of the outline of the high-speed transverse field modeand show trapezoidal comblike electrodes 5 tapered toward their tips asan exemplification. The shape of the comblike electrode 5 of the presentembodiment will be described later with reference to FIG. 9.

FIG. 5 shows a part of the second electrode E2 and liquid crystalmolecules LM in their initial alignment state in the liquid crystallayer LQ. A comblike electrode 5 of the second electrode E2 has a pairof first side 51 and second side 52 opposed to each other in the widthdirection (second direction Y) and a top side 53 bridging between thefirst side 51 and the second side 52. The first side 51 is inclinedclockwise at an acute angle θ (approximately 1.0 degrees, for example)with respect to the alignment treatment direction AD and second side 52is inclined counterclockwise at angle θ with respect to the alignmenttreatment direction AD. Furthermore, between two adjacent comblikeelectrodes 5, a base side 31 is formed by the connecting portion 3. Thebase side 31 and the first side 51 form a corner C1, the first side 51and the top side 53 form a corner C2, the base side 31 and the secondside 52 form a corner C3, and the second side 52 and the top side 53form a corner C4.

In an off-state where no voltage is applied between the first electrodeE1 and the second electrode E2, liquid crystal molecules LM are in theinitial alignment such that their longitudinal axes conform to thealignment treatment direction AD as shown in FIG. 5. That is, in theexample of FIG. 5, the initial alignment direction of the liquid crystalmolecules LM is parallel to the first direction X.

In an on-state where a voltage is applied between the first electrode E1and the second electrode E2, a field is produced between theseelectrodes. FIG. 6 shows equipotential lines of the liquid crystal layerLQ in the produced field. The equipotential lines represent thepotential on the X-Y plane at a certain height from the first alignmentfilm AL1, and a direction perpendicular to the equipotential linescorresponds to the direction of the field.

Equipotential lines near the first side 51 and the second side 52 becomesubstantially parallel to these sides in a middle area A1 of thecomblike electrodes 5 in the first direction X. Equipotential lines arebent at approximately 180 degrees in an arc shape along the shape of theslit SL in a base area A2 near the connecting portion 3. Furthermore,equipotential lines are bent at approximately 180 degrees in an arcshape along the shape of the comblike electrode 5 in a top area A3 nearthe top side 53.

FIG. 7 shows an alignment state of liquid crystal molecules LM in theon-state. The liquid crystal molecules LM of the present embodimentpossess positive dielectric anisotropy. Thus, upon application of avoltage between the first electrode E1 and the second electrode E2 inthe off-state in FIG. 5, a force is produced to rotate the liquidcrystal molecules LM in such a manner that their longitudinal axesbecome parallel to the direction of the field produced by theapplication of a voltage (or, their longitudinal axes become orthogonalto the equipotential lines).

In the proximity of corners C1 and C2, liquid crystal molecules LMrotate in a first rotational direction R1 which is indicated by a solidline. Furthermore, in the proximity of corners C3 and C4, liquid crystalmolecules LM rotate in a second rotational direction R2 which isindicated by a dotted line. The first rotational direction R1 isopposite to the second rotational direction R2. In the example of FIG.7, the first rotational direction R1 is counterclockwise and the secondrotational direction R2 is clockwise.

An alignment control function which controls a rotational direction ofliquid crystal molecules LM in the proximity of the first side 51 andthe second side 52 (in other words, an alignment stabilization function)is imparted to each of corners C1 to C4. That is, liquid crystalmolecules LM in the proximity of the first side 51 rotate in the firstrotational direction R1 according to the rotation of the liquid crystalmolecules LM in the proximity of corners C1 and C2. Liquid crystalmolecules LM in the proximity of the second side 52 rotate in the secondrotational direction R2 according to the rotation of the liquid crystalmolecules LM in the proximity of corners C3 and C4. Here, focusing onthe proximity of the center CR1 of the comblike electrode 5 and theproximity of the center CR2 of the slit SL in the second direction Y,the liquid crystal molecules LM rotating in the first rotationaldirection R1 and the liquid crystal molecules LM rotating in the secondrotational direction R2 counterbalance with each other. Therefore,liquid crystal molecules LM in the proximity of these centers aremaintained in their initial alignment state and rotate very little.

As can be understood from the above, in the high-speed transverse fieldmode, rotational directions of the liquid crystal molecules LM areregular from the base side 31 to the top side 53 in the proximity of thefirst side 51 and the second side 52. Consequently, the response speedin the application of a voltage can be increased, and alignmentstability can be improved because irregularity of rotational directionsof the liquid crystal molecules LM is suppressed.

Furthermore, even if the alignment of the liquid crystal molecules LM istemporarily disordered by an external impact, the alignment directionsof the liquid crystal molecules in the proximity of the first side 51and the second side 52 can be restored based on the works of the liquidcrystal molecules LM in the proximity of corners C1 to C4.

Furthermore, in the structure where comblike electrodes 5 a and 5 b arearranged alternately in the second direction Y as shown in FIGS. 2 and4, the first side 51 of the comblike electrode 5 a and the second side52 of the comblike electrode 5 b are basically aligned on the samestraight line and the second side 52 of the comblike electrode 5 a andthe first side 51 of the comblike electrode 5 b are basically aligned onthe same straight line in subpixel SPX. Furthermore, since the comblikeelectrodes 5 a and 5 b extend in opposite directions, the liquid crystalmolecules LM in the proximity of the first side 51 of the comblikeelectrode 5 a and the liquid crystal molecules LM in the proximity ofthe second side 52 of the comblike electrode 5 b rotate in the samedirection. Similarly, the liquid crystal molecules LM in the proximityof the second side 52 of the comblike electrode 5 a and the liquidcrystal molecules LM in the proximity of the first side 51 of thecomblike electrode 5 b rotate in the same direction. This means that therotational directions of the liquid crystal molecules become regular inthe entire comblike electrodes 5 a and 5 b in subpixel SPX, and theresponse speed can be increased more.

FIG. 8 shows luminosity distribution of light passing through a subpixelSPX in the on-state. On gray scale, the luminosity becomes higher inbrighter parts and becomes lower in darker parts. In the off-state ofFIG. 5, light incident on the first optical element OD1 partially passesthrough the first polarizer PL1 and enters the display panel PNL. Thelight which enters the display panel PNL is linearly polarized lightorthogonal to a first polarization axis of the first polarizer PL1. Thepolarization state of such linearly polarized light hardly changes whenpassing through the display panel PNL in the off-state. Therefore, thelinearly polarized light which passes through the display panel PNL isabsorbed by the second polarizer PL2 which is in a crossed-Nicolrelationship with the first polarizer PL1.

Conversely, a polarization state of light which passes through the firstpolarizer PL1 and enters the display panel PNL in the on-state shown inFIG. 7 changes when passing through the liquid crystal layer LQ based onan alignment state of liquid crystal molecules LM (or retardation in theliquid crystal layer). Therefore, the light which passes through theliquid crystal layer LQ partially passes through the second polarizerPL2 in the proximity of the first side 51 and the second side 52 wherethe liquid crystal molecules LM are rotated from their initial alignmentstate. Consequently, the luminosity in the proximity of the first side51 and the second side 52 becomes high as shown in FIG. 8. Conversely,the luminosity in the proximity of the center CR1 of the comblikeelectrode 5 and the center CR2 of the slit SL becomes low since theliquid crystal molecules LM therein rotate very little from theirinitial alignment state.

Note that the first side 51 and the second side 52 are inclined withrespect to the alignment treatment direction AD in the comblikeelectrodes 5 shown in FIGS. 5 to 8, and this structure helps theimprovement of the alignment stability. Specifically, in the proximityof the first side 51 and the second side 52 those are inclined withrespect to the alignment treatment direction AD, the direction of thefield crosses the alignment treatment direction AD at any angle exceptright angles, and thus, the rotational directions of the liquid crystalmolecules LM in the application of a voltage can be set substantiallyregular. As is evident from FIG. 6, the first side 51 and the secondside 52 are substantially parallel to the equipotential lines, and thus,the function of corners C1 to C4 weakens in the middle area A1. Thiswill be adverse to the alignment stability. However, with the first side51 and the second side 52 inclined with respect to the alignmenttreatment direction AD, excellent alignment stability can be secured inthe middle area A1.

For further improvement of the alignment stability, an angle formed bythe first side 51 and the second side 52 with the alignment treatmentdirection AD needs to be sufficiently large. However, securing asufficient angle is sometimes difficult for design limitation of pixelsand process limit of patterning. For example, the width of the comblikeelectrode 5 and the width of slit SL must be designed to be greater thanthe process limit. Therefore, if the arrangement pitch of each of thecomblike electrodes 5 in the second direction Y is small or the lengthof the comblike electrodes 5 is unchangeable, the comblike electrode 5cannot have a sufficient difference between the width at its base andthe width at its tip, and therefore, the angle formed by the first side51 and the second side 52 with the alignment treatment direction ADcannot be sufficiently large.

To deal with the above problem, the shape of the comblike electrode 5 isimproved in the present embodiment. FIG. 9 schematically shows a shapeof the comblike electrode 5 in the present embodiment. The figureexemplifies the comblike electrodes 5 a arranged with a pitch SP in thesecond direction and having a length L; however, the same shape can beapplied to the comblike electrode 5 b. For example, the comblikeelectrodes 5 a and comblike electrodes 5 b can be formed to besymmetrical with respect to an axis parallel to the second direction Y.

In the example of FIG. 9, the comblike electrode 5 a includes a firstpart P1, second part P2, and third part P3. The first part P1 is at thebase side of the comblike electrode 5 a (at the connecting portion 3side). The third part P3 is at the tip side of the comblike electrode 5a (at the top side 53). The second part P2 is between the first part P1and the third part P3.

The first side 51 is inclined at angle θ1 which is acute or zero in aclockwise manner with respect to the first direction X within the firstpart P1. The second side 52 is inclined at angle θ1 in acounterclockwise manner with respect to the first direction X within thefirst part P1. In the example of FIG. 9, angle θ1 is zero. That is, thewidth of the first part P1 is the same as the width W1 of the base ofthe comblike electrode 5 a (joint position with the connecting portion3) in the entirety of the first part P1.

The first side 51 is inclined at angle θ3 which is acute or zero in aclockwise manner with respect to the first direction X within the thirdpart P3. The second side 52 is inclined at angle θ3 in acounterclockwise manner with respect to the first direction X within thethird part P3. In the example of FIG. 9, angle θ3 is zero. That is, thewidth of the third part P3 is the same as the width W3 of the tip of thecomblike electrode 5 a (top side 53) in the entirety of the third partP3.

The first side 51 is inclined at angle θ2 which is acute in a clockwisemanner with respect to the first direction X within the second part P2.The second side 52 is inclined at angle θ2 in a counterclockwise mannerwith respect to the first direction X. That is, the width of the secondpart P2 gradually decreases from the first part P1 side toward the thirdpart P3 side. Angle θ2 is greater than both angles θ1 and θ3 (θ2>θ1 andθ3). For example, angle θ2 is greater than or equal to 0.5 degrees, andshould preferably be greater than or equal to 1.0 degrees.

A gap corresponding to a slit width WS is provided between the comblikeelectrode 5 a and the comblike electrode 5 b. In the example of FIG. 9,the slit width WS takes a positive value (WS>0); however, the slit widthSW may take a negative value (WS<0). In that case, a tip of a comblikeelectrode 5 b is inserted between a slit SL defined by a pair ofcomblike electrodes 5 a, and a tip of a comblike electrode 5 a isinserted between a slit SL defined by a pair of comblike electrodes 5 b.Alternately, the slit width WS may be zero (WS=0).

When a voltage is applied between the comblike electrodes 5 a with theabove structure and the first electrode E1, liquid crystal molecules LMin the proximity of the first part P1 and the third part P3 rotate inthe first rotational direction R1 or in the second rotational directionR2 by the function of corners C1 to C4 as explained above with referenceto FIGS. 5 to 8.

Conversely, the function of corners C1 to C4 weakens in the proximity ofthe second part P2. This is evident from the equipotential lines in themiddle area A1 which are substantially parallel to the first side 51 andthe second side 52 in FIG. 6. However, the first side 51 and the secondside 52 in the second part 2 are inclined at angle θ2 with respect tothe alignment treatment direction AD and excellent alignment stabilitycan be secured. That is, the liquid crystal molecules LM in theproximity of the first side 51 rotate regularly in the first rotationaldirection R1 and the liquid crystal molecules LM in the proximity of thesecond side 52 rotate regularly in the second rotational direction R2.

As described above, angle θ2 should preferably be set sufficiently largeto improve the alignment stability. In this respect, the comblikeelectrode 5 a in FIG. 9 is formed such that the first side 51 and thesecond side 52 in the first and third parts P1 and P3 are inclined withrespect to the alignment treatment direction AD at an angle smaller thanthose in the second part P2. Therefore, angle θ2 formed by the firstside 51 and the second side 52 with the alignment treatment direction ADin the second part P2 can be set large. Even if such factors as a designlimitation of pixels and a process limit of patterning restrict a changein length L, width W1 of the base, width W3 of the tip, and the like ofthe comblike electrode 5 a, excellent alignment stability can besecured.

Note that parameters of the comblike electrode 5 a including, forexample, length L1 of the first part P1 in the first direction X, lengthL2 of the second part P2 in the first direction X, length L3 of thethird part P3 in the first direction X, and angle θ2 can arbitrarily bedetermined based on the entire length L of the comblike electrode 5 a,pitch SP, thickness of the liquid crystal layer LQ, and the like.

The inventors studied the alignment stability in two cases: one is case(A) where a liquid crystal layer LQ having a thickness of 2.9 μmincludes rectangular comblike electrodes 5 each having a length of 10μm, and the other is case (B) where a liquid crystal layer LQ having thesame thickness includes rectangular comblike electrodes 5 each having alength of 15 μm. As a result, good alignment stability was confirmed incase (A) in the application of a voltage while alignment disorder wasconfirmed in case (B) in the application of a voltage. This is becausethe alignment control function of corners C1 to C4 was effective in theentirety of the first side 51 and the second side 52 in case (A) whilethe function did not work in the middle part of the first side 51 andthe second side 52 in case (B). According to this study, the limitationof lengths L1 and L3 is estimated to be somewhere between 5 to 7.5 μm toachieve excellent alignment stability under the conditions of cases (A)and (B). Therefore, lengths L1 and L3 should preferably be set less thanor equal to 5 μm. For example, if a comblike electrode 5 a has a lengthL of 21 μm, L1 and L3=5 μm and L2=11 μm.

Second Embodiment

Now, the second embodiment will be explained. Structural elements of thesecond embodiment which are the same as or similar to those of the firstembodiment will be referred to by the same reference numbers and theirdetails will be omitted.

FIG. 10 is a cross-sectional view which shows a part of the structure ofa liquid crystal display device DSP2 of the present embodiment. Theliquid crystal display device DSP2 includes a first electrode E1 whichfunctions as a common electrode and a second electrode E2 whichfunctions as a pixel electrode. In this respect, the liquid crystaldisplay device DSP2 differs from the liquid crystal display device DSP1.

The first electrode E1 is provided through subpixels SPXR, SPXG, andSPXB and includes openings 7 at positions corresponding to the secondelectrodes E2 in subpixels SPXR, SPXG, and SPXB.

Second electrodes E2 are provided with respective subpixels SPX. Eachsecond electrode E2 includes a plurality of slits SL. Furthermore, thesecond electrodes E2 are electrically connected to switching elements ofrespective subpixels SPXR, SPXG, and SPXB through the openings 7,contact holes CH1 formed in the first insulating layer 11, and contactholes CH2 formed in the second insulating layer 12.

FIG. 11 schematically shows a shape example applicable to the firstelectrode E1 of FIG. 10. In the example depicted, an area 8 opposed tothe second electrode E2 of each subpixel SPX is indicated by dottedlines.

The first electrode E1 includes the openings 7 at the positioncorresponding to both the contact holes CH1 and CH2. Except the openings7, the first electrode E1 is formed uniformly without a slit or thelike.

FIG. 12 schematically shows a shape example applicable to the secondelectrode E2 of FIG. 10. In the example depicted, the second electrodeE2 includes a connecting portion 3 extending along the second directionY and a plurality of comblike electrodes 5 (5 a, 5 b) extending fromboth sides of the connecting portion 3.

In the example of FIG. 12, the connecting portion 3 is formed in adouble-edged structure in which comblike electrodes 5 a extend from oneside of the connecting portion 3 (right edge) and comblike electrodes 5b extend from the other side of the connecting portion 3 (left edge).

Comblike electrodes 5 a and 5 b extend parallel to the first direction Xand are tapered toward their tips. In the present embodiment, comblikeelectrodes 5 a and 5 b extend in the direction conforming to thealignment treatment direction AD as in the above embodiment.

Comblike electrodes 5 a are arranged along the second direction Y withcertain intervals. Furthermore, comblike electrodes 5 b are arrangedalong the second direction Y with certain intervals. Spaces defined bycomblike electrodes 5 a and spaces defined by comblike electrodes 5 bcorrespond to the slits SL.

In the example of FIG. 12, comblike electrodes 5 a and 5 b are formed inthe same shape, and an arrangement pitch of each of comblike electrodes5 a adjacent in the second direction Y and an arrangement pitch of eachof comblike electrodes 5 b adjacent in the second direction are thesame. Comblike electrodes 5 a and 5 b are arranged alternately in thesecond direction Y.

Note that comblike electrodes 5 a and 5 b may be formed in differentshapes with different arrangement pitches. Furthermore, comblikeelectrodes 5 a and 5 b may not be arranged alternately in the seconddirection Y but may be arranged on the same lines.

A contact position 9 corresponds to the opening 7 and the secondelectrode E2 contacts the switching element SW at the contact position9.

The shape composed of the first part P1, second part P2, and third partP3 as shown in FIG. 9 can be applied to comblike electrodes 5 a. Thesame shape can be applied to comblike electrodes 5 b. For example, thecomblike electrodes 5 a and comblike electrodes 5 b can be formed to besymmetrical with respect to an axis parallel to the second direction Y.

Liquid crystal molecules LM in the proximity of comblike electrodes 5 aand 5 b act the same as described in the first embodiment. That is, asin FIG. 12 (a), when a voltage is applied between the first electrode E1and the second electrode E2, liquid crystal molecules LM in theproximity of the first side 51 of the comblike electrode 5 a rotate inthe first rotational direction R1 over the entire length of the firstside 51, and liquid crystal molecules LM in the proximity of the secondside 52 rotate in the second rotational direction R2 which is oppositeto the first rotational direction R1 over the entire length of thesecond side 52. Furthermore, as in FIG. 12 (b), liquid crystal moleculesLM in the proximity of the first side 51 of the comblike electrode 5 brotate in the second rotational direction R2 over the entire length ofthe first side 51, and liquid crystal molecules LM in the proximity ofthe second side 52 rotate in the first rotational direction R1 over theentire length of the second side 52.

As can be understood from the above, the high-speed transverse fieldmode can be achieved in the structure of the present embodiment.Furthermore, since comblike electrodes 5 a and 5 b include the firstpart P1, second part P2, and third part P3, the alignment stability canbe improved more.

In addition, the present embodiment can achieve the same advantagesobtained by the first embodiment.

Note that the structures of the first and second embodiments canarbitrarily be varied. Hereinafter, some of variations will beexplained.

Variation 1

In the examples of FIG. 2 and FIG. 12, the second electrode E2 is ofdouble-edged structure in which comblike electrodes 5 extend from bothsides of the connecting portion 3. However, the second electrode E2 maybe of single-edged structure in which comblike electrodes 5 extend fromeither side of the connecting portion 3.

FIG. 13 shows an example of the second electrode E2 of single-edgedstructure. The structure in this example is applied to the secondelectrode E2 which functions as a pixel electrode, and includes theconnecting portion 3 extending in the second direction Y and a pluralityof comblike electrodes 5 extending from either side of the connectingportion 3 parallel to the first direction X.

A single-edged structure can be applied to a second electrode E2 whichfunctions as a common electrode.

Variation 2

In the example of FIG. 9, the comblike electrode 5 has the first,second, and third parts P1 to P3. However, the comblike electrode 5 mayonly have the first and second parts P1 and P2. FIGS. 14 and 15 showexamples of the comblike electrode 5 of this variation.

A comblike electrode 5 shown in FIG. 14 has a first part P1 at its baseside (connecting portion 3 side) and does not have a third part P3.Conversely, a comblike electrode 5 shown in FIG. 15 has a first part atits tip side (top side 53) and does not have a third part P3.

In the first part P1 of both the examples of FIGS. 14 and 15, the firstside 51 is inclined clockwise at angle θ1 which is acute or zero withrespect to the first direction X, and the second side 52 is inclinedcounterclockwise at angle θ1 with respect to the first direction X. Inthese examples, angle θ1 is zero.

Even if the third part P3 is omitted as in this variation, angle θ2 inthe second part P2 can be set large because of the first part P1. Thus,good alignment stability can be secured in the proximity of the secondpart P2. Note that, by setting the length L1 of the first part P1 suchthat corners C1 and C3 perform the alignment control functionsufficiently in the example of FIG. 14 and such that corners C2 and C4perform the alignment control function sufficiently in the example ofFIG. 15, the alignment stability in the proximity of the first part P1can also be secured.

Variation 3

In the first and second embodiments, the structures adoptable in caseswhere liquid crystal molecules of the liquid crystal layer LQ possesspositive dielectric anisotropy are exemplified. However, the liquidcrystal layer LQ may be formed of liquid crystal molecules possessingnegative dielectric anisotropy. In that case, the alignment treatmentdirection AD (or the initial alignment direction of liquid crystalmolecules) is set to a direction orthogonal to the extension of comblikeelectrodes 5 and slits SL.

Several embodiments of the present application have been presentedabove; however, they are examples of the present application and nolimitation to the scope of invention is intended thereby. The novelembodiments described above can be achieved in other various models, andas long as they stay within the scope of the invention, can be achievedwith various omission, replacement, and modification to their details.The embodiments and variations are encompassed by the scope and conceptof the invention and included within the range equal to the inventionsrecited in the claims.

What is claimed is:
 1. A display device comprising: a first substrateincluding a first electrode, an insulating layer covering the firstelectrode, a second electrode opposed to the first electrode with theinsulating layer interposed therebetween, and a first alignment filmcovering the second electrode; a second substrate including a secondalignment film opposed to the first alignment film; and a liquid crystallayer including liquid crystal molecules sealed between the firstalignment film and the second alignment film, wherein the secondelectrode includes a plurality of comblike electrodes extending parallelto a first direction and tapered toward tips thereof, and a connectingportion which connects the comblike electrodes, an initial alignmentdirection of the liquid crystal molecules is parallel to the firstdirection or a second direction which is orthogonal to the firstdirection, the comblike electrode includes a first part having sidesopposed to each other in the second direction each form a first anglewith the first direction, and a second part having sides opposed to eachother in the second direction each form a second angle with the firstdirection, the second angle being greater than the first angle, and thecomblike electrode has the first part at the tip side and the secondpart at the connecting portion side.
 2. The display device of claim 1,wherein a length of the first part is less than or equal to 5 μm.
 3. Thedisplay device of claim 1, wherein the first angle is substantiallyzero.
 4. The display device of claim 1, wherein the second angle isgreater than or equal to 1.0 degree.
 5. The display device of claim 1,wherein the liquid crystal molecules have positive dielectricanisotropy, and the initial alignment direction is parallel to the firstdirection.
 6. The display device of claim 1, wherein the comblikeelectrodes include a plurality of first comblike electrodes extendingfrom the connecting portion in the first direction and arranged alongthe second direction, and a plurality of second comblike electrodesextending from the connecting portion in the direction opposite to thefirst direction and arranged along the second direction.
 7. The displaydevice of claim 6, wherein the first comblike electrodes and the secondcomblike electrodes are symmetrical with respect to an axis parallel tothe second direction.
 8. The display device of claim 6, wherein thefirst comblike electrodes and the second comblike electrodes arearranged alternately in the second direction.
 9. The display device ofclaim 1, wherein the first substrate is provided with a plurality ofsubpixels, the second electrode is provided over the plurality ofsubpixels and includes an aperture closed by the connecting portion, andthe comblike electrodes are arranged in the aperture.